Woollacott Robert M, Zimmer Russel L
Museum of Comparative Zoology Laboratories, Harvard University, Cambridge, Massachusetts 02138.
Santa Catalina Marine Biological Laboratory, University of Southern California, Avalon, California 90704.
J Morphol. 1975 Nov;147(3):355-377. doi: 10.1002/jmor.1051470308.
Embryos of the marine cheilo-ctenostome bryozoan Bugula neritina undergo a marked increase in volume (about 500-fold) during embryogenesis while being retained in a brood chamber. Previous morphological studies indicate that shortly after transfer of the zygote to the brood chamber, the epithelium of the maternally-derived portion of the brood chamber, the ooecial vesicle, differentiates in regions adjacent to the embryonary space from a squamous to a columnar form suggesting that the parent is involved as a source of extraembryonic nutrients required for the extensive growth of the embryo. Results of the present ultrastructural study indicate that hypertrophy of the epithelial cells occurs only in that region of the ooecial vesicle which opposes the embryo, that differentiation (and subsequent regression) of the lining are predictable events correlated with the onset (and termination) of embryonic growth, and that hypertrophied cells are well equipped for the synthesis and transport of macromolecular materials across the vesicle wall to the developing embryo. Further, that portion of the embryo's ectoderm (the presumptive metasomal sac) in contact with this hypertrophied epithelium is morphologically specialized for the uptake of nutrients. Finally, shortly before release of the larva, this intimate association of the metasomal sac tissue and the hypertrophied ooecial vesicle lining epithelium is terminated by invagination of the sac and atrophy of the lining.
海洋唇口目苔藓虫类的布氏苔藓虫（Bugula neritina）胚胎在胚胎发育过程中，体积会显著增大（约500倍），同时一直留在育卵室中。先前的形态学研究表明，在合子转移到育卵室后不久，育卵室中母源部分即卵囊泡的上皮，在与胚胎空间相邻的区域从鳞状分化为柱状，这表明母体作为胚胎大量生长所需的胚外营养来源发挥了作用。本次超微结构研究结果表明，上皮细胞肥大仅发生在卵囊泡与胚胎相对的区域，内衬的分化（以及随后的退化）是与胚胎生长开始（和终止）相关的可预测事件，并且肥大细胞具备合成和跨囊泡壁向发育中的胚胎转运大分子物质的良好能力。此外，胚胎外胚层与这种肥大上皮接触的部分（假定的后体囊）在形态上专门用于摄取营养。最后，在幼虫释放前不久，后体囊组织与肥大的卵囊泡内衬上皮的这种紧密联系通过囊的内陷和内衬的萎缩而终止。
